1. Technical Field
The present invention relates to a virtual image display system such as a head-mounted display mounted on a head of an observer.
2. Related Art
In related art, a virtual image display system (image display system) having an appearance of eyeglasses for an observer to observe an image formed by a display device such as an LCD (Liquid Crystal Display) as a virtual image using an optical system has been proposed (for example, see Patent Document 1 (JP-A-2006-162767)).
The virtual image display system disclosed in Patent Document 1 has a structure in which an image display unit having a display device (LCD or the like), a projection lens (objective lens), etc. and a light guide plate (substrate) are fixed to an eyeglass frame.
On the light guide plate, an entrance mirror and a combiner are respectively provided at one end side and the other end side.
The entrance mirror reflects image light output from the display device and projected by the projection lens as parallel light so that the image light may be totally reflected within the light guide plate and guided to the combiner.
Then, the combiner reflects the image light guided by the total reflection within the light guide plate and guides it to a predetermined position (the left eye or the right eye of the observer) outside of the light guide plate.
In the above described virtual image display system, in order to guide the image light to the left eye or the right eye of the observer in good condition (for the observer to observe the image in good condition), the positional relationship between the projection lens (optical axis) and the light guide plate (entrance mirror) is very important.
However, in the virtual image display system disclosed in Patent Document 1, a positioning structure for positioning the light guide plate with respect to the projection lens is not provided.
Therefore, in assembly of the virtual image display system, it is necessary to move the image display unit and the light guide plate to positions where the image may be observed in good condition while actually observing the image light, and then, fix the image display unit and the light guide plate to the eyeglass frame.
That is, there is a problem that positioning of the light guide plate with respect to the projection lens becomes complicated.
Further, in the virtual image display system disclosed in Patent Document 1, there is a problem that, for example, when the above described positioning structure is provided between an outer casing of the image display unit and the eyeglass frame, it is difficult to accurately position the light guide plate with respect to the projection lens.
Specifically, a holding member such as a lens tube for holding the projection lens, the outer casing of the image display unit, and the eyeglass frame intervene between the projection lens and the light guide plate to be positioned. That is, there are many members intervening between the projection lens and the light guide plate to be positioned, and manufacturing tolerances of the intervening members or the like are accumulated and the light guide plate tends to be displaced from the desired position with respect to the projection lens in assembly of the virtual image display system.